The 158M Dual Sine-Sawtooth Generator is a dual VCO sine wave that can be wave shaped to a sawtooth. The frequency range of the VCO is 5 Hz to 20 KHz and is adjusted by a front panel control or switched to an external CV. There is also an AC coupled FM input with an attenuator control. The input jack is normaled to the opposite oscillator.

The 158 requires both +15V and +24V.

Operation

The original module consisted of one PCB but the MEMS version has a panel PCB to minimize front panel wiring. The panel PCB also has a 15V:24V DC-DC converter.

Operation

This VCO is a ramp core with circuitry to convert to a triangle and shape to a sine. As such there is a small notch in the top of the triangle that shows in the sine. At 5 Hz the triangle is a bit distorted which affects the shape of the sine.

The waveshape circuit morphs the sine to a saw.

At the upper frequency of 20 KHz, the reset time becomes more predominant as can be seen in this scope image. 

The ramp becomes more distorted at this upper frequency.

This scope image shows the sine waveform at 1 KHz.

And the saw at the same frequency.

The FM input jack is normaled to the opposite oscillator so you can FM one oscillator by the other. These next four scope images show the sine wave folding with increasing FM. Note this is similar in architecture to the timbre circuit in the 1973 208. The only difference is those two oscillators track together while the 158 has to be adjusted to the same frequency. This scope image shows a minimal amount of folding.

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